Giant acoustic atom: A single quantum system with a deterministic time delay

Abstract

We investigate the quantum dynamics of a single transmon qubit coupled to surface acoustic waves (SAWs) via two distant connection points. Since the acoustic speed is five orders of magnitude slower than the speed of light, the travelling time between the two connection points needs to be taken into account. Therefore, we treat the transmon qubit as a giant atom with a deterministic time delay. We find that the spontaneous emission of the system, formed by the giant atom and the SAWs between its connection points, initially decays polynomially in the form of pulses instead of a continuous exponential decay behaviour, as would be the case for a small atom. We obtain exact analytical results for the scattering properties of the giant atom up to two-phonon processes by using a diagrammatic approach. We find that two peaks appear in the inelastic (incoherent) power spectrum of the giant atom, a phenomenon which does not exist for a small atom. The time delay also gives rise to novel features in the reflectance, transmittance, and second-order correlation functions of the system. Furthermore, we find the short-time dynamics of the giant atom for arbitrary drive strength by a numerically exact method for open quantum systems with a finite-time-delay feedback loop.

Non-Markovian dynamics of a qubit due to single-photon scattering in a waveguide

“…A distinctive feature of our open dynamics is that the bath (the waveguide field) is initially in a well-defined single-photon state [43,44]. Toward this task, we tackle in full the time evolution of multiple excitations (in contrast to those limited to the one-excitation sector [43,[45][46][47][48]), a problem that has become important recently [30,31,33,[49][50][51][52][53][54][55][56][57].Intuitively, one may expect that the dynamics is fully Markovian in the infinite-waveguide case and NM in the semi-infinite case due to the atom-mirror delay time. We show that this expectation is inaccurate in general, mostly because it does not account for a fundamental source of NM behavior namely the wavepacket bandwidth.…”

Semiclassical analysis of dark-state transient dynamics in waveguide circuit QED

“…In this section, we start from the circuit-QED Hamiltonian of the system in the continuum limit and connect to a quantum optical system-reservoir approach, where both the transmon qubit and the TL degrees of freedom are quantized. In this model, one degree of freedom of the qubit is directly coupled to the field amplitude in one point and it has been used frequently in literature [29,30]. We find a direct connection between this model and the above equations of motion in the low impedance TL regime.…”

“…This result is consistent with the derivation shown in refs. [30,42] and leads to the same dynamics. However it is crucial to note that the behaviour of the qubit energy in the case of high impedance cannot be modeled with this approach.…”

A unidirectional on-chip photonic interface for superconducting circuits

“…In analogy to "giant" artificial atoms [20][21][22][23], which couple to a photonic or phononic waveguide at several points separated by distances comparable to the wavelength, our approach consists in designing a giant unidirectional emitter (GUE), here realized using two artificial atoms as anharmonic oscillators, as represented in Fig. 1(a).…”